220 Chapter 7
Digital Signal Interface Module
Clock Timing
The clock source is selected using the N5102A module UI on the signal generator, see Figure 7-2.
Figure 7-2 Clock Source Selection
When you select a clock source, you must let the N5102A module know the frequency of the clock signal
using the
Clock Rate softkey. In the internal clock source mode, use this softkey to set the internal clock rate.
For device and external clock sources, this softkey must reflect the frequency of the applied clock signal.
When the clock source is Internal, a frequency reference must be applied to the Freq Ref connector. The
frequency of this applied signal needs to be specified using the Reference Frequency softkey, unless the
current setting matches that of the applied signal.
The selected clock source provides the interface module output clock signal at the Clock Out and the Device
Interface connectors.
Common Frequency Reference
The clocking flexibility of the digital signal interface module allows the setting of arbitrary clock rates for
the device under test. In general, the clock rate inside the ESG will be different from the interface module
clock rate, so the interface module performs a rate conversion. An important aspect of this conversion is to
have accurate clock rate information to avoid losing data. The module relies on relative clock accuracy,
instead of absolute accuracy, that must be ensured by using a single frequency reference for all clock rates
involved in the test setup. This can be implemented in various ways (see the five drawings in Figure 7-3 on
page 222), but whatever way it is implemented, the clock inside the signal generator must have the same
base frequency reference as the clock used by the device under test.
External and Device selection:
Set to match the clock rate
of the applied clock signal
Internal selection: Set the
internal clock rate
Internal clock source
selection: Set the frequency
of the applied reference
signal.
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